taxonomy – Questionable Evolution

Storage & Survival in the Palm Family

Palm trees have had to develop some creative strategies to survive drought and cool climates.

My recent work with Botany One writing news briefs for newly published botany research has had me reading a lot of scientific articles, and it just so happens that twice in the last couple of weeks, they’ve dealt with new research on palms. Having worked mostly on legumes as a researcher, I’d never given much thought to these fascinating plants, beyond the fact that they look good on a tropical beach. But there’s a lot to them, as I’ve been finding out lately, and I thought I’d write a little post to share what I’ve learned.

Palms are members of the Arecaceae family, which has around 2600 species spread through the world’s tropical and subtropical regions. They are monocots, like grasses or orchids. The arborescent, or tree-like, members of the palm family – what we’d call a palm tree – are unique among tall trees in that they have no vascular cambium. This is the cell layer in the trunk of a tree that allows it to widen year upon year, and is also responsible for tree growth rings. If you cut a palm tree down, there are no annual rings in its trunk, because that trunk didn’t continue to grow. (It’s also why their trunks look so cylindrical, as opposed to the usual tapering you see in a tree trunk.) This imposes some interesting restrictions on the tree. For instance, the tree’s vasculature cannot be renewed, as it is in other trees. The cells making up the tubes that transport water and nutrients through the trunk must last the entire life of the tree, which can be upwards of 100 years in some species.

While more than 90% of palms are restricted to tropical rainforests, some also occur in cool, high altitude regions and arid deserts. Unlike most of the plants that live in cool and dry habitats, palms lack dormancy mechanisms, such as dropping their leaves, that would help them to survive these conditions. What’s more, like all monocots, palms have no central tap root that will allow them to reach deeper reserves of soil water. So they’ve had to develop some creative survival strategies. Under drought conditions, which some palm trees endure regularly due to their arid habitat, the greatest danger to a plant is vascular embolism. This happens when the water column that runs through the plant breaks because there’s not enough water, and air bubbles form and expand through the xylem tubes. Once a certain amount of air is present in the tube, it will never function again and the tissue it feeds will die. To help counter this, palm trees store water in parenchyma cells adjacent to the xylem, so that when an embolism is imminent, more water can be shifted into the column. Their anatomy also encourages embolisms that do happen to happen closer to the tip of the leaf, as opposed to near or inside the trunk, where they would do greater damage.

Palms have a neat survival trick to help their seeds germinate in the low temperatures. Most palms store oil in their seeds to provide sustenance for the seedling when it germinates. This is usually high in saturated fats, which aren’t liquid at low temperatures. This would mean that seeds either couldn’t germinate under cool conditions, or would risk starvation if they did. New research has found that palms growing in cooler climates have evolved their own oil blend rich in unsaturated fats, which are liquid at lower temperatures, to help their seeds thrive in those habitats.

Speaking of oil storage, palms have been hugely important to human beings since before the dawn of civilization, all thanks to those oils, which can occur in both the seed and the fruit, and provide a high calorie food source. The best known is coconut, Cocos nucifera, with its greasy, delicious seed, which we eat as a fruit. In fact, the fruit of a coconut isn’t a nut at all, it’s a drupe. But while coconut is perhaps the most familiar palm food, the most economically important is certainly the oil palm, genus Elaeis. The oil that comes from this palm is high in saturated fat, making it useful for deep-frying (and bio-fuel), if not the best for your health. The use of palm oil is controversial, because of the environmental and human rights abuses linked to its production, yet production is ongoing in regions of Africa, Asia, and the Americas. Outside of their oil production, palms are also the source of dates, palm syrup, carnauba wax, and wood.

Recent research has found that the seeds with the greatest oil storage are all grouped in the tribe Cocoseae, but that palms with oily fruits and moderately oily seeds abound throughout the family, suggesting there may yet be nutritionally and economically valuable species that haven’t been discovered, though whether the further exploitation of these resources is a welcome development is debatable.

What’s in a Name?

Part Two: How’s Your Latin?

295738_obamadon_f — The awesomely named *Obamadon gracilis*. Image: Reuters

What do Barack Obama, Marco Polo, and the band Green Day have in common? They all have at least one organism named after them. Obama has several, including a bird called Nystalus obamai and an extinct reptile named Obamadon gracilis. Green Day’s honorary organism is the plant Macrocarpaea dies-viridis, “dies-viridis” being Latin for “green day.” Many scientists also have species named after them, usually as recognition for their contributions to a field. My own PhD advisor, Dr. Anne Bruneau, has a genus of legumes, Annea, named after her for her work in legume systematics.

Nashi_pear — “Pear-leaved Pear” Photo via Wikimedia Commons

Scientific names, which are colloquially called Latin names, but which often draw from Greek as well, consist of two parts: the genus, and the specific epithet. The two parts together are called the species. Though many well-known scientists, celebrities, and other note-worthies do have species named after them, most specific epithets are descriptive of some element of the organism or its life cycle. Many of these are useful descriptions, such as the (not so bald) bald eagle, whose scientific name is the more accurate Haliaeetus leucocephalus, which translates to “white-headed sea eagle.” (See here for some more interesting examples.) A few are just botanists being hilariously lazy with names, as in the case of Pyrus pyrifolia, the Asian pear, whose name translates as “pear-leaved pear.” So we know that this pear tree has leaves like those of pear trees. Great.

In contrast to common names, discussed in our last post, Latin names are much less changeable over time, and do not have local variants. Soybeans are known to scientists as Glycine max all over the world, and this provides a common understanding for researchers who do not speak the same language. Latin is a good base language for scientific description because it’s a dead language, and so its usage and meanings don’t shift over time the way living languages do. Until recently, all new plant species had to be officially described in Latin in order to be recognized. Increasingly now, though, descriptions in only English are being accepted. Whether this is a good idea remains to be seen, since English usage may shift enough over the years to make today’s descriptions inaccurate in a few centuries’ time.

This isn’t to say that scientific names don’t change at all. Because scientific names are based in organisms’ evolutionary relationships to one another (with very closely related species sharing a genus, for example), if our understanding of those relationships changes, the name must change, too. Sometimes, this causes controversy. The most contentious such case in the botanical world has been the recent splitting of the genus Acacia.

Acacia is/was a large genus of legumes found primarily in Africa and Australia (discussed previously on this blog for their cool symbiosis with ants). In Africa, where the genus was first created and described, the tree is iconic. The image of the short, flat-topped tree against a savanna sunset, perhaps accompanied by the silhouette of a giraffe or elephant, is a visual shorthand for southern Africa in the popular imagination, and has been used in many tourism campaigns. The vast majority of species in the genus, however, are found in Australia, where they are known as wattles. When it became apparent that these sub-groups needed to be split into two different genera, one or the other was going to have to give up the name. A motion was put forth at the International Botanical Congress (IBC) in Vienna in 2005 to have the Australian species retain the name Acacia, because fewer total species would have to be renamed that way. Many African botanists and those with a stake in the acacias of Africa objected. After all, African acacias were the original acacias. The motion was passed, however, then challenged and upheld again at the next IBC in Melbourne in 2011. (As a PhD student in legume biology at the time, I recall people having firm and passionate opinions on this subject, which was a regular topic of debate at conferences.) It is possible it will come up again at this year’s IBC in China. Failing a major turnaround, though, the 80 or so African acacias are now known as Vachellia, while the over one thousand species of Australian acacias continue to be known as Acacia.

The point of this story is, though Latin names may seem unchanging and of little importance other than a means of cataloguing species, they are sometimes both a topic of lively debate and an adaptable reflection of our scientific understanding of the world.

Do you have a favourite weird or interesting Latin species name? Make a comment and let me know!

What’s in a Name?

Part One: Common vs. Scientific Names

img_3146-staghornsumac

When I was a kid growing up on a farm in southwestern Ontario, sumac seemed to be everywhere, with its long, spindly stems, big, spreading compound leaves, and fuzzy red berries. I always found the plant beautiful, and had heard that First Nations people used the berries in a refreshing drink that tastes like lemonade (which is true… here’s a simple recipe). But often, we kids were warned by adults that this was “poison sumac,” not to be touched because it would give us itchy, burning rashes, like poison ivy did. In fact, plenty of people would cut down any nascent stands to prevent this menace from spreading. We were taught to fear the stuff.

Toxicodendron_vernix#1978a#2_400 — THIS is the stuff you need to look out for. Via The Digital Atlas of the Virginia Flora

It was many years later before I learned that the red-berried sumacs I grew up with were not only harmless, but were also not closely related to the poisonous plant being referred to, which, as it turns out, has white berries and quite different leaves. Scientifically speaking, our innocent shrub is Rhus typhina, the staghorn sumac, while the rash-inducing plant is called Toxicodendron vernix. Not even in the same genus. Cautious parents were simply being confused by the similarity of the common names.

This story illustrates one of the ironies of common names for plants (and animals). Though they’re the way nearly everyone thinks of and discusses species, they’re without a doubt the most likely to confuse. Unlike scientific (Latin) names, which each describe a single species and are, for the most part, unchanging, a single common name can describe more than one species, can fall in and out of use over time, and may only be used locally. Also important to note is that Latin names are based on the taxonomy, or relatedness, of the species, while common names are usually based on either appearance, usage, or history.

This isn’t to say that common names aren’t valuable. Because common names describe what a plant looks like or how it is used, they can convey pertinent information. The common names of plants are also sometimes an important link to the culture that originally discovered and used the species, as in North America, where native plants all have names in the local languages of First Nations people. It seems to me, although I have no hard evidence to back it up, that these original names are now more often being used to form the Latin name of newly described species, giving a nod to the people who named it first, or from whose territory it came.

One high profile case of this in the animal world is Tiktaalik roseae, an extinct creature which is thought to be a transitional form (“missing link”) between fish and tetrapods. The fossil was discovered on Ellesmere Island in the Canadian territory of Nunavut, and the local Inuktitut word “tiktaalik”, which refers to a type of fish, was chosen to honour its origin.

But back to plants… Unlike staghorn sumac and poison sumac, which are at least in the same family of plants (albeit not closely related within that family), sometimes very distinct species of plants can end up with the same common name through various quirks of history. Take black pepper and bell or chili peppers. Black pepper comes from the genus Piper, and is native to India, while hot and sweet peppers are part of the genus Capsicum. Botanically, the two are quite distantly related. So why do they have the same name? Black pepper, which bore the name first, has been in use since ancient times and was once very highly valued. The confusion came about, it would seem, when Columbus visited the New World and, finding a fruit which could be dried, crushed, and added to food to give it a sharp spiciness, referred to it as “pepper” as well.

Sa-pepper — A black peppercorn. Easy to confuse with a chili pepper, I guess? Via: Wikimedia Commons

Another interesting, historically-based case is that of corn and maize. In English-speaking North America, corn refers to a single plant, Zea mays. In Britain and some other parts of the Commonwealth, however, “corn” is used to indicate whatever grain is primarily eaten in a given locale. Thus, Zea mays was referred to as “Indian corn” because it was consumed by native North Americans. Over time, this got shortened to just “corn”, and became synonymous with only one species. Outside of Canada and the United States, the plant is referred to as maize, which is based on the original indigenous word for the plant. In fact, in scientific circles, the plant tends to be called maize even here in North America, to be more exact and avoid confusion.

1024px-Spanish_moss_at_the_Mcbryde_Garden_in_hawaii — Not Spanish, not a moss. Via: Wikimedia Commons

And finally, for complete misinformation caused by a common name, you can’t beat Spanish moss. That wonderful gothic stuff you see draped over trees in the American South? That is neither Spanish, nor a moss. It is Tillandsia usneoides, a member of the Bromeliaceae, or pineapple family, and is native only to the New World.

And that wraps up my very brief roundup of confusing common names and why they should be approached with caution. In part two, I’ll discuss Latin names, how they work, and why they aren’t always stable and unchanging, either.

There are SO many more interesting and baffling common names out there. If you know of a good one, let me know in the comments!

*Header image via the University of Guelph Arboretum